Volume indicator



May 31, i938. H. KAHL VOLUME INDICATOR Filed sept. 4,l 1957 2 sheets-sneer 1 May 31, 193s. H. AHL

VOLUME INDICATOR Filed Sept. 4, 1937 2 Sheets-Sheet 2 s.. l. 0 9 7. 5 5 4. 2 l l. 0. 0 0 0 0, 0 0 0 PLATE VOL 7s, E@

CURRENT AT WHICH "TR/GEER TUBE OPERA TES GR/D BIAS -VOLTS ATTQRA/Ey Patented May 31, 1938 UNITED STATES PATENT oFFllcE Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application September 4, 1937, Serial No. 162,416

9 Claims.

This invention relates to telephone exchange systems and more particularly to systems in which a subscriber by calling a particular line designation may obtain a connection with a centraltime announcing system over which at specific intervals announcements are made by a special operator of the correct time of day.

It is the object of the invention to enable the announcing operator to maintain the volume of her announcements within a desired range.

In general, volume indicators employ some type of graduated dial by which the operator may make an estimate of the volume of the announcements. In accordance with the present invention, an indicator is provided which by a lampsignal indicates to the operator that the voice level is satisfactory. In the control of this indication, applicants volume indicator employs a pentode' tube operated at a low plate voltage range wherein the plate current changes rapidly with a small change in the applied grid voltage, the critical grid voltage being determined by the adjustment of the screen grid voltage. Following response .at a lirst level, the indicator is reset by means of a gas-filled tube to respond at a second level.

The invention will be more clearly understood from a consideration of the following description in connection with the drawings in which:

Fig. l discloses the volume indicator circuit as applied to a time of day announcement trunk, and

Figs. 2 and 3 show the characteristics of the direct-current amplifier used.

The time of day announcement trunk may conveniently be of the type disclosed in Patent 1,863,141 granted June 14, 1932 to W. B. Prince. The reference numerals of the six-hundred series appearing on the drawings refer to similar apparatus disclosed and described in this patent.

When the announcing operator comes on duty she connects her announcing transmitter 60| by inserting plug 603 into jack 606 of the desk circuit and consequently relay 609 is operated over a make spring of jack 606. Likewise relay 6|!) is operated in the circuit from battery through the right winding of relay 6|0, sleeves of jack 606 and plug 603, transmitter 60|, tips of plug 603 and jack 605, right windings of repeating coil 6|| to ground through the left winding of relay 6|0. Relay 6I0 in turn initiates a chain of operations resulting in the operation of relay 6|'l as deand causing lamp 624 to light as a signal to the operator that a call for time of day has been initiated by a calling subscriber. Under the control of the clock circuit |00 ground is connected to conductor 63| in order to light lamp 630 at such a time that the lighting of the lamp 630 is a signal to the operator that she should announce into her transmitter 60| the time indicated before her by a clock (not shown) controlled from the clock circuit |00. A predetermined interval thereafter ground is connected to conductor 128, winding of relay 632 and battery, operating relay 632 to connect tone to the trunk to mark the exact time as described in the Prince patent. The volume indicator VI may be connected in any desired manner across the announcing trunk at the output of the repeater 615.

The volume indicator circuit is rst carefully calibrated for the proper speech volume before it is connected into service. This `is accomplished asfollows: The plug connected to source |5|, of 1000 cycle one milliwatt standard testing power, is inserted in jack |52 thus disconnecting the volume indicator from the desk circuit and operating relay ||4. The `filaments of the vacuum tubes of the volume indicator are then heated by operating key |02 to its middle position, connecting battery |44 through low resistance |03 over the right and left contacts, of key |02 and through resistances |04, |05, |06 and |01 to ground, the filaments of the tubes |08, |00 and ||0 being connected around resistances |05, |06 and |01, respectively. When the filaments have become heated, key |02 is thrown to the right thereby substituting ballast lamp for resistance |03. The heating current is then adjusted to the proper value by means of a milliammeter connected into jack |45. When the tubes are ready, key |53 is operated closing obvious circuits for relays I I5 and H6. The locking of relay H5 is prevented by blocking open the upper normal contacts of relay H6. With relay ||4 operated, lamp |54 is lighted in a circuit from battery through lamp |54, lower alternate contacts of relay H4, upper normal contacts of relay |33 to ground at the lower front contact of relay H6.

The current from the test source |5| is first amplified by the full wave rectifier tube |08 and the output from the tube |08 is applied to the control grid of the direct current amplifier pentode |09, the output of which is applied to the input of the trigger tube I0. Condenser I3| is normally charged from battery |42 through lamp |32 and resistance |30. Potentiometer |46 is then adjusted until tube ||0 just breaks down and completes a discharge circuit for condenser I 3| extending from ground over the cathodeanode circuit of tube I|0, upper front contact of relay |I5, lower back contact of relay |29, lower winding of relay ||'I to condenser |3I. Relay Y II'I operates in this circuit and locks in a circuit from battery through its upper winding and upper front contact to ground on conductor IIB. It also extends its locking ground to the winding of relay |29 which operates, opening the op-Y erating circuit of relay II'I. Relay |29 .connects grounded conductor IIB over the inner upper front contact of relay |29 to the winding of relay |33 and battery. Relay |29 .also opens the discharge circuit of tube ||0 thereby extinguishing it. With relay |33 operated the test lamp |54 is extinguished. If necessary, the tap on the secondary winding of transformer IOI may be adjusted Ato bring about the desired operation. After the adjustments have been made they may be tested by momentarily releasing key |53 to reset the circuit. After Calibrating the circuit, key |53 is restored, the contact of relay ||6 is released and plug |50 is removed from jack |52 thus putting the volume indicator into service with the input of repeating coil |0| connected across the output of repeating coil 615 of the desk circuit. With key ||2 normal, relay ||3 is operated holding its contact normally closed.

As previously stated, at the beginning of each announcement period which occurs every fteen seconds, ground is connected to conductor 63| by the clock circuit |00 thereby completing a circuit over the outer upper contact of test relay ||4 through the upper winding of relay ||5 to battery. Relay I| 5 locks in a circuit from battery through its lower winding and inner lower front contact to ground through the normal contacts of relay |I6. The operation of relay I|5 closes one point in the circuit of relay II'I and connects ground to conductor ||8 preparing locking circuits for relays II'I and I I9. Y

During the announcement, the volume indicator receives a portion of theY speech current as it emerges from the desk repeater 615 by means vof repeating coil I0.|. This speech current is rst amplied by the full wave rectifier tube |08 which also acts as a buffer so that no modulation current, resulting from the rectication of the speech by the diodes |20 and |2| of tube |08 will interfere with the announcement. The output from the full wave rectifier is supplied to the network N, comprising resistances |22 to |25 and condensers |21 and |28, which modifies the potential so that the potential iiuctuates exactly as would the pointer of a dial type volume indicator. This fluctuating potential is applied to the control grid of the direct current amplier pentode |09 which acts as a voltage amplifier. The trigger type tube I |0 indicates any volume in excess of a certain amount, for example, one decibel, by breaking down. Condenser I 3| was previously charged from battery |42 through lamp |32 and resistance |30. When tube I|0 breaks down it completes a discharge circuit for condenser |3| extending from ground over the cathode-anode circuit of tube |I0, upper front contact of relay II5, lower back contact of relay |29, lower winding of relay to condenser |3I. Relay operates in this circuit and locks in a circuit from battery through its upper winding and upper front contact to ground on conductor IIB. VIt also extends its locking ground to the winding of relay |29 which operates, opening the operating circuit of relay I|'I. Relay |29 connects grounded conductor ||8 over the inner upper front contact of relay I 29 to the winding of relay |33 and battery. Relay |29 also opens the discharge circuit of tube ||0 thereby extinguishing it. It also transfers the connection of the grid of pentode |09 from the right terminal of resistance |25 to the mid-point of that resistance.

It may be noted that the cathode of tube |09 is connected to conductor |34, while the grid of tube |09 is normally connected over the back contact of relay |29 to a point between resistances |25 and |24 so that the input circuit of tube |09 is connected across resistance |25. Following the operation of relay |29 the connection of the grid of tube |69 is transferred to the mid-point of resistance |25 so that the input circuit now is connected across only half of the resistance |25. This change in the connection of the control grid of tube |09 reduces the fluctuating voltage supplied thereto by approximately 6 decibels. The operation of relay |33 opens the circuit oi lamp |4| and connects the plate of tube ||0 over the front contacts of relays ||5 and |33, upper back contact of relay |35, inner upper back contact of relay |36, lower winding of relay IIS to resistance |31 and condenser |38. Condenser |38 is charged by battery through lamp |32 and resistance |37 in the same manner as was condenser |3|. If now the volume of speech is such as to be in excess of 6 decibels higher than the low critical volume, the trigger tube ||0 again breaks down thus causing the operation of relay 9 by closing a discharge path for condenser |38. Relay Y|| 9 locks in a circuit from battery through its upper winding and inner upper front contact, the normally closed contact of relay I I3 to grounded conductor II 8 and extends its locking ground to the winding of relay |36'. Relay |36 operates in turn closing a circuit from battery through the winding of relay |35, left normal contacts of key ||2, upper front contact of relay I 36 to ground over the lower right normal contacts of key II2. Relay |35 locks over its lower front contact to the ground over the lower back contact of relay I I6, and opens the discharge circuit for tube |I0 and the operating circuit of relay |I9.

Immediately after the announcement, the associated clock circuit connects ground to conductor '|23 for approximately one-half second and disconnects ground from conductor 63|. The connection of ground to conductor |28 operates relay IIS over the middle upper contact of relay ||4. The disconnection of ground from conductor 63| opens the operating circuit of relay |I5 and with relay ||6 operated, relay I I5 now releases. The operation of relay |I6 supplies a substitute holding ground for conductor Il, holding relays |33, |29, ||9 and |36 operated, thereby completing a circuit from battery through lamp |39, inner upper contact of relay H4, lower front contact of relay |36 to ground over the inner upper normal contacts of key ||2, causing lamp |39 to be lighted while relay ||6 is held operated. The lighting of lamp |39 indicates to the operator when the speech volume is too high. The removal of ground from conductor '|28 releases relay ||S thus extinguishing lamp |39 and releasing relays |33, |29, II'I, ||9 and |36 restoring the circuit to normal.

If the operators voice is not of sufficient volume when making the announcement the trigger tube ||0 will not break down at all. Under this conpreviously described, but will not Yoperate relays H and |30 `and neither lamp will light, indicating to the operator that the Volume of her speech was satisfactory.

In this volume indicator, the tubes |00 and H0 operate underrfairly normal conditions and in the conventional manner. However, important advantages are obtained by operating the tube |09 at a very low plate voltage, a condition which results in non-linear amplication. The plate voltage is supplied from source |42 which is +130 volts and is connected to the plate through the resistance |43 which is 500,000 ohms. 'Ihe screen grid voltage is adjusted to approximately +36 volts, being supplied by a potentiometer included in the circuit from the -48 volt battery |44, ballast lamp III, contacts of jack |45, contacts of key |02, potentiometer |46 and ground. The cathode is connected through resistance |41 `and ballast lamp I I to source |44 while the control grid is connected to the filament through a one-megohm resistance |48. With no signal applied, current flovvs through the anode-cathode circuit and while the control grid is at zero potential with respect to the filament, the plate is only slightly positive. The cathode of the trigger tube I I0 being directly grounded is biased 48 volts positive with respect to the cathode of tube |09, therefore the effective negative bias on the trigger tube grid is about 4'7 volts. As the control grid of tube |09 iscarried negative by an incoming signal, the plate voltage changes by only an inappreciable amount for biases up to about 3.5 volts, and at 4.0 volts the plate voltage has risen only to about +15. However, an increase in the signal voltage to 4.5 volts carries the plate voltage up to about +48 volts or the potential of the trigger tube cathode, causing the latter to break down. Thus the tube |09 differentiates very sharply between signals relatively close together in amplitude and the individual characteristics of the trigger tube becomes relatively unimportant in determining the signal level at which the latter will be tripped. The characteristic curves of Fig. 2 illustrate the principles involved in the action of tube |00. In this gure the load line AB gives the relationship between the instantaneous plate voltage and plate current under the operating conditions.

Besides serving to distinguish clearly between signals of very nearly the same amplitude, tube |09 has an additional advantage over a three-element vacuum tube for this use. By adjusting the screen grid voltage suitably, the gain of the circuit may be adjusted conveniently and precisely and in addition the effects of the manufacturing variations between tubes can be eliminated for all practical purposes. The characteristic curves of Fig. 3 indicate hovv the response of tube |09 may be varied by the adjustment of the screen grid voltage due to the adjustment of the potentiometer |40.

What is claimed is:

1. In a sound volume indicator, a sound current carrying channel, a high resistance, means for establishing a potential across said resistance proportional to the volume of sound current in said channel, indicating means normally connected across said resistance comprising a direct current amplier anda gas-filled discharge tube responsiverto a predetermined potential, and means controlled by said gas-filled discharge tube for connecting said indicating means across a portion of said resistance.

2. In a sound volume indicator, a sound current carrying channel, a high resistance, means for establishing a potential across said resistance proportional to the volume of sound current in -said channel, indicating means normally connect- Ved across said resistance comprising a direct current amplifier and a gas-filled discharge tube responsive to a predetermined potential, and means controlled by said gas-filled discharge tube for v connecting said indicating means across a portion of said resistance and for resetting said gas-filled discharge tube.

3. In a sound volume indicator, a sound current carrying channel, a high resistance, means for establishing a potential across said resistance proportional to the volume of sound current in said channel, indicating means normally connected across said resistance comprising a direct current amplier and a gas-iilled discharge tube responsive to a predetermined potential, means controlled by said gas-filled discharge tube for connecting said indicating means across a portion of said resistance and for resetting said gaslled discharge tube, a lamp, and means for lighting said lamp responsive to the second functioning of said discharge tube. Y

4. In a sound volume indicator, a sound current carrying channel, a high resistance, means for establishing a potential across said resistance proportional to the volume of sound current in said channel, indicating means normally connected across said resistance comprising a direct current amplifier and a gas-lled discharge tube responsive to a predetermined potential, means -controlled by said gas-filled discharge tube for connecting said indicating means across a p0rtion of said resistance and for resetting said gaslled discharge tube, two lamps, means for lighting one of said lamps if said discharge tube fails to function, and means to light the other of said lamps if said discharge tube functions in response to the connection of said indicating means across the portion of said resistance. 5. In a sound volume indicator, a sound current carrying channel, a high resistance, means for establishing a potential across said resistance proportional to the volume of sound current in said channel, indicating means normally connected across said resistance comprising a direct current amplier and a gas-filled discharge tube responsive to a predetermined potential, means controlled by said gas-filled discharge tube for connecting said indicating means across a portion of said resistance and for resetting said gas-lled discharge tube, and time controlled means for resetting said volume indicator following each application of sound current to said channel.

6. In a sound volume indicator, a sound current carrying channel, a high resistance, means for establishing a potential across said resistance proportional to the volume of sound current in said channel, indicating means normally connected across said resistance comprising a direct current amplifier and a gas-iilled discharge tube responsive to a predetermined potential, means controlled by said gas-filled discharge tube for connecting said indicating means across apor tion of said resistance and for resetting said gaslled discharge tube, a lamp, means for lighting said lamp responsive to the second functioning of said discharge tube, and time controlled means for resetting said volume indicator following each application of sound current to said channel.

7. In a sound volume indicator, a. sound current carrying channel, a high resistance, means for establishing a potential across said resistance proportional to the volume of sound current in said channel, indicating means normally connected across said resistance comprising a direct current amplifier and a gas-lled discharge tube responsive to a predetermined potential, means controlled by said gas-filled discharge tube for connecting said indicating means across a portion of said resistance and for resetting said gas-lled discharge tube, two lamps, means for lighting one of said lamps if said discharge tube fails to function, means to light the other of said lamps if said discharge tube functions in response to the connection of said indicating means across the portion of said resistance, and time controlled means for resetting said volume indicator following each application of sound current to said channel.

8. In a sound volume measuring system, a source of sound current, means for generating a potential proportional to the volume of said sound, and means for indicating when said potential exceeds a predetermined Value comprising a vacuum tube having at least a cathode, an anode and a control electrode, a gas-filled trigger tube having a cathode, an anode and a control electrode, the anode of said vacuum tube being connected to the control electrode of said trigger tube, means for operating said vacuum tube at a relatively low anode potential to render said vacuum tube sensitive to critical input potentials, means for applying said sound generated potentials to the control electrode of said vacuum tube, and indicating means connected to the anode of said trigger tube.

9. In a volume measuring system, a source of sound current, means for generating a potential proportional tothe volume of said sound and means for indicating when said potential exceeds a predetermined value comprising a vacuum tube having at least a cathode, an anode, a control electrode and a screen electrode, a gas-filled trigger tube having a cathode, an anode and a control electrode, the anode of said vacuum tube being connected to the control electrode of said trigger tube, means for operating said vacuum tube at a relatively loW anode potential to render said vacuum tube sensitive to critical input potentials, means for applying said sound generated potentials to the control electrode of said vacuum tube, indicating means connected to the anode of said trigger tube, and means for controlling the volume at which said indicating means shall be responsive comprising means for applying a potential to said screen electrode and means for adjusting said potential to a desired value.

HENRY KAHL. 

